Integrated front projection system with enhanced dry erase screen configuration

ABSTRACT

A front projection screen and associated system and method are disclosed that utilize a back structured layer and a front diffusing layer to provide improved viewable image quality. The structured layer is formed with a plurality of grooves and can operate to direct light into a defined audience view region. The diffusing layer is coupled to the structured layer and is formed from a matte polyester film to provide dry erase capability on a front surface of the diffusing layer. For example, the matte polyester film can be TEKRA Marnot XL matte Melinex polyester film. Further, the structured layer can be formed as an acrylate linear prismatic structure having a gloss white coating. The acrylate linear prismatic structure and the matte polyester film can be coupled, for example, by lamination or can be coupled by being extruded as a unitary construction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.09/616,563, filed on Jul. 14, 2000 and entitled “Integrated FrontProjection System,” which is a continuation of application Ser. No.09/261,715, filed Mar. 3, 1999 issued as U.S. Pat. No. 6,179,426.

BACKGROUND OF THE INVENTION

The present invention relates to an integrated front projection displaysystem. In particular, the present invention relates to a low-profileintegrated front projection system that coordinates specializedprojection optics and an integral screen optimized to work inconjunction with the optics to create the best viewing performance andproduce the necessary keystone correction.

Electronic or video display systems are devices capable of presentingvideo or electronically generated images. Whether for use inhome-entertainment, advertising, videoconferencing, computing,data-conferencing or group presentations, the demand exists for anappropriate video display device.

Image quality remains a very important factor in choosing a videodisplay device. However, as the need increases for display devicesoffering a larger picture, factors such as cost and device size andweight are becoming vital considerations. Larger display systems arepreferable for group or interactive presentations. The size of thedisplay system cabinet has proven an important factor, particularly forhome or office use, where space to place a large housing or cabinet maynot be available. Weight of the display system also is an importantconsideration, especially for portable or wall-mounted presentations.

Currently, the most common video display device is the typical CRTmonitor, usually recognized as a television set. CRT devices arerelatively inexpensive for applications requiring small to medium sizeimages (image size traditionally is measured along the diagonaldimension of a rectangular screen). However, as image size increases,the massive proportions and weight of large CRT monitors becomecumbersome and severely restrict the use and placement of the monitors.Also, screen curvature issues appear as the screen size increases.Finally, large CRT monitors consume a substantial amount of electricalpower and produce electromagnetic radiation.

One alternative to conventional CRT monitors is rear projectiontelevision. Rear projection television generally comprises a projectionmechanism or engine contained within a large housing for projection upon the rear of a screen. Back-projection screens are designed so thatthe projection mechanism and the viewer are on opposite sides of thescreen. The screen has light transmitting properties to direct thetransmitted image to the, viewer.

By their very nature, rear projection systems require space behind thescreen to accommodate the projection volume needed for expansion of theimage beam. As background and ambient reflected light may seriouslydegrade a rear projected image, a housing or cabinet generally enclosesthe projection volume. The housing may contain a mirror or mirrors so asto fold the optical path and reduce the depth of the housing. The needfor “behind-the-screen” space precludes the placing of a rear projectiondisplay on a wall.

A new category of video presentation systems includes so-called thinPlasma displays. Much attention has been given to the ability of plasmadisplays to provide a relatively thin cabinet (about 75-100 mm deep),which may be placed on a wall as a picture display in an integratedcompact package. However, at the present time, plasma displays 3 arecostly and suffer from the disadvantages of low intensity (approx.200-400 cd/m² range) and difficulty in making repairs. Plasma displaypanels are heavy (about 80-170 lb, about 36-77 kg), and walls on whichthey are placed may require structural strengthening.

A traditional type of video presentation device that has not receivedthe same degree of attention for newer applications is front-projectionsystems. A front-projection system is one that has the projectionmechanism and the viewer on the same side of the screen. Frontprojection systems present many different optical and arrangementchallenges not present in rear projection systems, as the image isreflected back to the audience, rather than transmitted. An example offront projection systems is the use of portable front projectors and afront projection screen, for use in meeting room settings or inlocations such as an airplane cabin.

One of the advantages of front projectors is the size of the projectionengine. Electronic front projectors traditionally have been designed forthe smallest possible “footprint”, a term used to describe the areaoccupied on a table or bench, by the projector. Portable frontprojectors have been devised having a weight of about 10-20 lb (about4.5-9 kg).

Nevertheless, front projection systems have traditionally not beenconsidered attractive for newer interactive applications because offactors such as blocking of the image by the projector or the presenter,poor image brightness, image distortion and setup 2o difficulties.

Traditional electronic front projectors typically require a room thatmay afford the projection volume necessary for image expansion withoutany physical obstructions. Although images may be projected upon a largeclear flat surface, such as a wall, better image quality is achieved bythe use of a separate screen. FIGS. 1 and 2 illustrate a traditionalfront projection system. A projector 10 is placed on a table or otherelevated surface to project an image upon a screen or projection surface20. Those familiar with the use of electronic projectors will appreciatethat tilting the projector below the normal axis of the screen producesa shape distortion of the image, known as a keystone effect. Most newelectronic projectors offer a limited degree of keystone correction.However, as may be appreciated in FIG. 2, the placement of the projectormay still interfere with the line of sight of the audience.

Of greater significance is the fact that to achieve a suitable imagesize, and also due to focus limitations, the projector 10 requires acertain “projection zone” in front of the screen 20. Table A lists thepublished specifications for some common electronic projectors currentlyin the market.

TABLE A Smallest Shortest Maximum Projector Lens Focal Imager ScreenThrow Throw Keystone Type Length Diagonal Diagonal Distance RatioCorrection CTX Opto * 163 mm 1.0 m 1.1 m 1.1 20° offset/ ExPro 580Transmis- optical sive LCD InFocus * 18 mm 1.3 m 1.5 m 1.2 18° offsetLP425 Reflective DMD Chisholm 43-58.5 23 mm 0.55 m 1.2 m 2.2 15° Dakotamm Reflective electronic X800 LCD Epson 55-72 mm 33.5 0.58 m 1.1 m 1.9 *Powerlite Transmis- 7300 sive LCD Proxima 45-59 mm 23 mm 0.5 m 1.0 m 2.012° offset Impression Transmis- A2 sive LCD 3M 167 mm 163 mm 1.0 m 1.2 m1.2 16° offset/ MP8620 Transmis- optical sive LCD *Not given inpublished specifications

Throw distance is defined as the distance from the projection lens tothe projection screen. Throw ratio usually is defined as the ratio ofthrow distance to screen diagonal. The shortest throw distance availablefor the listed projectors is one meter. To achieve a larger image,between 40 to 60 inches (about 1 to 1.5 meters), most projectors must bepositioned even farther away, at least 8 to 12 feet (about 2.5 to 3.7meters) away from the wall or screen.

The existence of this “projection zone” in front of the screen preventsthe viewer from interacting closely with the projected image. If thepresenter, for example, wishes to approach the image, the presenter willblock the projection and cast a shadow on the screen.

Traditional integrated projectors require optical adjustment, such asfocusing every time the projector is repositioned, as well as mechanicaladjustment, such as raising of front support feet. Electronicconnections, such as those to a laptop computer, generally are madedirectly to the projector, thus necessitating that the projector bereadily accessible to the presenter or that the presenter runs thenecessary wiring in advance.

Another problem with front projectors is the interference by ambientlight. In a traditional front projector a significant portion of theprojected light is scattered and is not reflected back to the audience.The loss of the light results in diminished image brightness.Accordingly, a highly reflective screen is desirable. However, the morereflective the screen, the larger the possible degradation of theprojected image by ambient light sources. The present solution, whenviewing high quality projection systems such as 35 mm photographic colorslide presentation systems, is to attempt to extinguish an ambientlights. In some very critical viewing situations, an attempt has beenmade even to control the re-reflection of light originating from theprojector itself.

Some screen designers have attempted to address the ambient lightproblem with “mono-directional reflection” screens, that is, aprojection screen attempts to absorb fight not originating from theprojector, while maximizing the reflection of incident light originatingfrom the direction of the projector. Nevertheless, since portableprojectors are, in fact, portable and are used at various throwdistances and projection angles, it has proven very difficult tooptimize a screen for all possible projector positions and opticalcharacteristics.

An alternative is to design a dedicated projection facility. Such adesign necessitates a dedicated conference room, in which the projectorand screen position, as well as the projector's optical characteristics,are rigorously controlled and calibrated. Structural elements may beused to suspend the selected projector from the ceiling. Oncecalibrated, such system would be permanently stationed. Such a facilitymay suffer from high costs and lack of portability.

Another issue that prevents optimal performance by front projectors isthe keystone effect. If projectors are placed off-center from thescreen, keystone distortion will occur. Keystone distortion is aparticular image distortion where the projection of a rectangular orsquare image results in a screen image that resembles a keystone, thatis a quadrilateral having parallel upper and lower sides, but said sidesbeing of different lengths.

Methods for the reduction of keystone distortion again are dependentupon the position of the projector with respect to the screen. Keystonecorrection may be achieved by optical and by electronic methods. Forlarge keystone correction in LCD imagers, optical methods are presentlypreferable, as electronic methods may suffer from pixelation distortion,as pixels become misaligned. Presently, to the applicants' knowledge,the available optical keystone correction in commercially availableportable electronic front projectors is between 10° to 20°.

The need remains for a large screen video presentation system thatoffers efficient space utilization, lower weight and attractive pricing.Such a system should preferably yield bright, high-quality images inroom light conditions. Furthermore, improved screen configurations aredesirable to provide enhanced image resolution and brightness.

SUMMARY OF THE INVENTION

The present invention provides an enhanced screen configuration for aprojection screen that improves the viewable image quality.

According to one aspect of the present invention, a front projectionscreen comprises a back structured layer and a front diffusing layer.The structured layer is formed with a plurality of grooves and canoperate to direct light into a defined audience view region. Thediffusing layer is coupled to the structured layer and is formed from amatte polyester film to provide dry erase capability on a front surfaceof the diffusing layer. For example, the matte polyester film can beTEKRA Marnot XL matte Melinex polyester film. Further, the structuredlayer can be formed as an acrylate linear prismatic structure having agloss white coating. The acrylate linear prismatic structure and thematte polyester film can be coupled, for example, by lamination or canbe coupled by being extruded as a unitary construction.

In addition, the present invention is an associated front projectionsystem. The front projection system may include a projection devicecoupled to the projection screen. In addition, the projection device maybe movably coupled, and may be an arm that moves from a closed,non-projection position to an open, projection position.

Still further, the present invention is an associated method ofprojection an image into a desired viewable space. This method mayinclude structured layer and a diffusing layer, as described above andin more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a traditional projection device andscreen arrangement.

FIG. 2 is an elevation side view of the arrangement illustrated in FIG.1.

FIG. 3 is a perspective view of an integrated front projection system inaccordance with the present invention in the use or projection position.

FIG. 4 is a perspective view of the integrated front projection systemillustrated in FIG. 3 in the closed or storage position.

FIG. 5 is a side elevation view of the integrated front projectionsystem illustrated in FIG. 3 in the use or projection position.

FIG. 6 is a schematic cut-away side elevation view of a first embodimentof the arm and projection head of the integrated front projection systemillustrated in FIG. 3.

FIG. 7 is a schematic cut-away side elevation view of a secondembodiment of the arm and projection head of the integrated frontprojection system illustrated in FIG. 3.

FIG. 8 is a side elevation view of a third embodiment of an integratedfront projection system in accordance with the present invention in theuse or projection position.

FIG. 9 is a schematic cut-away side elevation view of a fourthembodiment of the arm and projection head of an integrated frontprojection system in accordance with the present invention.

FIG. 10 is a schematic cut-away side elevation view of a fifthembodiment of the arm and projection head of an integrated frontprojection system in accordance with the present invention.

FIG. 11 is a top plan view of the integrated front projection systemillustrated in FIG. 10.

FIG. 12 is a perspective view of a sixth embodiment of an integratedfront projection system in accordance with the present invention.

FIG. 13 is a perspective view of a seventh embodiment of an integratedfront projection system in accordance with the present invention.

FIG. 14 is a side elevation view of the vertical reflection pattern of acontrolled light distribution front projection screen in accordance withthe present invention.

FIG. 15 is a plan view of the horizontal reflection pattern of the frontprojection system illustrated in FIG. 14.

FIG. 16 is a vertical cross-sectional view of a controlled lightdistribution front projection screen in accordance with the presentinvention.

FIG. 17 is a horizontal cross-sectional view of the front projectionscreen illustrated in FIG. 16.

FIG. 18 is a perspective view of a portion of the honeycomb structure ofthe integrated front projection system illustrated in FIG. 3.

FIG. 19 is a detail plan view of the portion of the honeycomb structureillustrated in FIG. 18.

FIGS. 20-21 are a side elevation view and a top elevation view ofanother embodiment of a projection screen and its defined lightdistribution according to the present invention.

FIGS. 22-25 are front elevation, side cross-section and cut-awayperspective views of the projection screen of FIGS. 20-21 showing moredetail of the front diffusing layer and back structured layer accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention comprises a frontprojection system that integrates an optical engine, having modularcontrol and power supply electronics, and a dedicated projection screento provide a compact and light video display device. FIGS. 3-6illustrate a first exemplary embodiment of an integrated frontprojection system 100 in accordance with the present invention.

The front projection system 100 includes a dedicated high gainprojection screen 102 mounted on a frame 104. A projection head 106 ispivotally mounted by an arm 108 to a center top portion of the frame 104at a hinge unit 110. The arm 108 may be rotated out 90′ allowing theprojection head 106 to pivot from a closed or storage position to anopened or projection position.

The screen 102 is optically coupled to the projection head. The screen102 may be a flexible material extended over frame 104 or may be a rigidcomponent. In an alternative embodiment, both the screen and the frameare made of an integral sheet of material. The screen 102 may includemultiple-layers or special coatings, such as to allow its use as anerasable whiteboard.

The frame 104 contains and supports other components of the system. Theframe 104 may house additional components such, as integrated speakers112, input and output jacks 113, and a control panel 114. In the presentexemplary embodiment, the mechanical infrastructure of the projectionsystem 100, the arm 108 and the frame 104, include lightweight materialssuch as aluminum magnesium or plastic composites. The entire projectionsystem, accordingly, is relatively light (20-25 pounds, 9-11 kilograms).

In the present exemplary embodiment, the arm 108 is rigid and hollow.The arm 108 comprises die cast aluminum or magnesium, or other suitablematerials, surrounded by a hard plastic shell. At the top and center ofthe frame 104, the hinge unit 10 allows the projection arm 108 and head106 to pivot between a closed (storage) position and an open (use)position. FIG. 4 illustrates the projection system 100 in a closed orstorage position. When not in use, the arm 108 may be kept in the closedposition as to be substantially parallel with the frame 104, and thuspresent no obstruction to objects that may be moving in the space infront of the frame 104. Although the arm is shown folded back to anaudience left position, the system may be adaptable to allow storage ofthe arm and projection head to an audience fight position. An ability toselect storage position may be valuable in avoiding obstacles present inthe projection area prior to the installation of the system. The abilityof the arm 108 to rotate contributes to the projection system's minimalthickness, approximately 2-3 inches (5-7.5 cm), in the storage position.

The system 100 allows for the projection head 106 to be placed in anexact pivotal registration in the operating or projection mode inrelation to the optical screen 102. In system 100, use position is at anormal arm angle with respect to the screen and generally above thescreen. However, other embodiments may be designed around otherpredetermined positions. Movement between the two positions may beassisted manually or may be motor-driven.

In the present embodiment, an electrical motor 116 residing within thehinge unit 110 controls the movement of the arm 108. The motor 116 maybe AC, DC, manually driven by détentes, over-center-cam (spring loaded)or any other suitable type that provides reliable repeatablepositioning. The motor 116 is a precision guided gear drive motor havingtwo limit sensor switches to accurately position the arm 108, andaccordingly, the projection head 106, in precise and repeatable closedand open positions.

The movement of the arm 108 and the functions of the projector system100 may be controlled through the control panel 114, a remote control(not shown), or other control mechanism. While the arm 108 of theprojection system 100 is pivotally fixed at a single point, thoseskilled in the art will readily appreciate that a variety of differentlinkage and/or pivoting mechanisms may be implemented within the spiritof the present invention. In alternative embodiments, the head and armmay include additional hinge or telescopic movement and the arm may becoupled to other portions of the frame or to a wall or post.

As explained in more detail in relation to FIGS. 14-17, the system 100optimizes the coupling of the projection engine with the exactpositioning of the head 106 in relation to the screen 102 to yield highcontrast, brightest enhancement, image uniformity, optimal imageposition, and sharp focus. Since the optical parameters of theprojection engine are known and selected for compatibility and the exactposition of the projector head 106 in the use position is known andpredetermined, the exemplary screen 102 may be designed and optimized toprovide maximum illumination for the audience while reducinginterference by ambient light.

When active, the projection system 100 generates a beam of light havinga plurality of light rays 162. In relation to a coordinate systemwherein the screen defines a z-plane, each fight ray 162 includescomponents along both the horizontal x-plane and the vertical y-plane.The angle of incidence of each light beam 162 upon the screen 102depends on the optical characteristics of the projector, such asf-number, and the position of the projection head 106 in relation to thescreen 102.

FIG. 14 is a side elevation of a vertical axis ray diagram, illustratingthe reflection of tight beams 162 emitted by projection system 100.Point 60 is the known precise location of the ideal point source forprojection lens 140 (illustrated in FIG. 6) when the projection head 106is in the “USE” position. The angles of incidence of the light beams 162on the screen increase along the positive x-direction (see directionalaxis in FIG. 14).

In a traditional screen, the light rays 162 would each be reflected inaccordance with their angle of incidence. Especially at the sharpprojection angle of system 100, the resulting light pattern would bescattered, with only a portion of the light rays reaching the audience.To compensate for the graduated increase in incidence angles, the screen102 includes a vertically graduated reflection pattern oriented toreceive the projected light rays 162 at the expected incidence angle foreach point on the screen 102 and to reflect the rays approximately atnormal angle along the vertical plane. The light beams 162 are reflectedin a direction vertically close to normal because that corresponds tothe expected location of the audience. In alternative embodiments wherethe audience is expected to be in a different position, a differentreflection pattern may be implemented.

FIG. 15 illustrates a top plan view of the horizontal distribution ofthe fight emanating from point 60. As the audience is expected to behorizontally distributed, the horizontal reflection pattern of thescreen is arranged to provide a wider illumination spread in thehorizontal direction.

FIG. 16 illustrates an expanded view of a vertical cross-section of theprojection screen 104. FIG. 17 illustrates an expanded plan view of ahorizontal cross section of the screen. The projection screen comprisesa multi-layer material. The screen 104 includes a first linear Fresnellens element 170, a second linear Fresnel element 172, and a reflectivecomponent 174. First and second spacer elements 171 and 173 may beplaced between the Fresnel elements 170 and 172 and between the secondFresnel element 172 and the reflective element 174 respectively. Thelinear Fresnel lens elements 170 and 172 include a planar side, 176 and178 respectively, and a prismatic side, 180 and 182 respectively. Thefirst Fresnel element 170 includes a thin isotropic diffusing layer 184on its planar side 176. The diffusing layer 184 functions as animage-receiving surface. The prismatic side 180 includes a plurality oflinear grooves 186 running horizontally in a graduated pattern. Thegrooves 186 are designed to control the vertical light spread. The lenscenter is positioned near the top of the projection screen.

The prismatic side 182 of the second linear Fresnel lens element 172includes a plurality of vertical grooves 188 (FIG. 17) facing theplurality of grooves 186 of the first Fresnel lens element 170. Thesecond linear Fresnel lens element 172 has a lens center positioned on avertical line extending through the center of the screen. The planarsurface 178 of second Fresnel element 172 faces a back reflector 174,having a vertical linear structure reflecting the light back in thedirection of the audience. The grooves of the structure back reflector174 preferably have a cylindrical shape, such as a lenticular structure,or may be a repeating groove pattern of micro facets that approximate acylindrical shape. An incident surface 175 of the back reflector 174 maybe specular or diffuse reflecting, metallic, or white coated, dependingon the amount of screen gain and type of screen appearance desired.Second linear Fresnel element 172, in conjunction with the structuredback reflector 174, provides control light distribution spreading in thehorizontal direction to accommodate viewers who are positionedhorizontally in front of the screen. Alternatively, the reflectorstructure 174 may be embossed into the planar is surface 178, reducingthe number of screen elements.

Alternative embodiments of the screen may comprise 3M multi-layer filmtechnology, such as described in U.S. Pat. No. 6,018,419, assigned to3M.

FIGS. 20-25, for example, illustrate another embodiment of a frontprojection screen 800, according to the present invention. In general,projection screen 800 can be used with the present integrated projectionsystem and, as such, is designed for off-axis projection at a shortthrow distance. Further, projection screen 800 has a wide-angledistribution of light in the horizontal direction, and a controllednon-symmetric distribution of light in the vertical direction to adefined audience view region 804. Projection screen 800 can have Moiréelimination for projected matrix image, and also can provide a planarand durable front surface that allows for cry erasable whiteboardcapability. It can also can be a single integral element and be readilymanufactured.

FIGS. 20 and 21 are a side elevation view and a top elevation view ofprojection screen 800 and its defined light distribution. As shown, aprojection device lens 802 can project an image onto projection screen800, and the image is then reflected for viewing within a view region804, which is bounded in part by points A and B. Projection screen 800has a surface diffusing layer 806 on the front surface and a whitereflecting horizontal microprismatic structured layer 808 on the backsurface, which layer 808 directs light into the defined verticalaudience view region 804. The diffusing layer 806 on the front surfacecan serve a dual purpose of spreading the reflected light fromstructured layer 808 and of preventing first surface reflection of thelight source from projection lens 802 to the viewing region 804.

More particularly, FIG. 20 represents a projection system that is anoff-axis system. In such a system, the image is being directed to thescreen 800 at a sharp angle that is not aligned with a perpendicularaxis of the screen 800 (i.e., off-axis projection). The screen 800,therefore, desirably directs the reflected light into the viewing area804.

FIG. 21 represents a projection system that is on-axis. In such asystem, the image is being directed to the screen 800 in alignment witha perpendicular axis of the screen 800 (i.e., on-axis projection). Thescreen 800 in FIG. 21 also desirably directs reflected light into theviewing area. However, in this on-axis projection configuration, thescreen requirements need not be as demanding as the off-axis projectionscreen to provide as good a viewable image quality.

FIGS. 22-25 show more details of an embodiment for screen 800, includingdiffusing layer 806 and microprismatic structured layer 808, thatprovides enhanced viewable image quality. In particular, FIGS. 22-25 arefront elevation, side cross-section and cut-away perspective views ofprojection screen 800 showing more detail of diffusing layer 806 andstructured layer 808.

In the depicted embodiment, the pitch of the reflecting microprismaticgrooves can be chosen to minimize projected Moire from a known pitchmatrix imager. There also may be no bulk diffusers to distribute lightin either the horizontal or vertical directions, thereby substantiallyeliminating screen scintillation or speckle problems. Projection screen800 can be replicated as a single element, without any lamination ofmultiple components. Further, the diffusing layer 806 can function as awriting surface for dry erase pens when formed, for example, from aTEKRA Marnot XL matte Melinex polyester film or CLAREX DR-IIIC lightdiffusion filter with an applied dry erase coating, as described below.

Looking now to FIG. 22, an example projection screen 800 is depicted.This projection screen 800 may have a 4:3 aspect ratio, for example, 48inches (122 cm) wide by 36 inches (91.4 cm) high, and can have aplurality of horizontal grooves 809 (represented by the horizontaldashed lines) which provide the horizontal microprismatic structure ofthe reflective structured layer 808. In this embodiment, grooves 809 areeach characterized by a riser and an edge. And the structure andorientation of grooves 809 change depending upon their location within adistance “Y” from the top of projection screen 800.

FIG. 23 is a side cross-section view of diff-using layer 806 andstructured layer 808 near the top of projection screen 800 (for example,Y=0.5 mm). As shown, structured layer 808 comprises grooves 809 having ariser 810 and an edge 812. In contrast, FIG. 24 is a side cross-sectionview of diffusing layer 806 and structured layer 808 near the bottom ofprojection screen 800 (for example, Y=920.5 mm). At the bottom ofprojection screen 800, riser 810 and edge 812 can be quite differentfrom that shown in FIG. 23 near the top of projection screen 800. It isnoted that these geometry's and the change from top to bottom of grooves809 may be selected so that the vertical light distribution is intoviewing region 804.

FIG. 25 is a cut-away perspective view of projection screen 800 showingan additional feature of projection screen 800. FIG. 25 shows a ripple814 formed in the surface of riser 810 and edge 812 that is transverseto the direction of grooves 809. This ripple 814 provides for increasedlight spread in the horizontal direction and may be formed by anoscillating master cutting tool.

In the embodiment of FIGS. 20-25, diffusing layer 806 preferablyprovides a dry erasable front matte projection surface while, inalternative embodiments, diffusing layer 806 can provide a high gainsilver layer or other non dry erasable surface appropriate for frontprojection screens. To provide the dry erase capability, diffusing layer806 can be formed from a TEKRA Marnot XL matte Melinex polyester film.This polyester film can be laminated to an acrylate linear prismaticstructure layer 808, which in turn has a gloss white coating and anoptional adhesive backing. Alternatively, the TEKRA polyester filmdiffusing layer 806 and structured layer 808 could be extruded to form aunitary construction with no separate, laminated layers. In conjunctionwith the diffusing layer 806, the horizontal prismatic grooves 809 onstructured surface 808 are designed to direct reflected light verticallyto a defined viewing region 804, as discussed above. Additionalspreading is controlled by the matte front surface of diffusing layer806, and by optional curving of the linear prismatic grooves 809.Further, a linear ripple pattern such as that of FIG. 25 can be used toincrease light spread in the horizontal direction.

Another material that can be used to form a dry erasable diffusing layer806 is a bulk white diffusing plastic, such as a CLAREX DR-IIIC lightdiffusion filter. In this case, a dry erase coating is applied to thefront surface and linear horizontal prismatic grooves 809 formed in theback surface of the CLAREX material. Grooves 809 can then be withaluminum or similar mirror coating to control the reflected distributionof light in the vertical direction. Again, a ripple pattern can be usedto enhance the light spread in the horizontal direction.

In one exemplary embodiment, projection screen 800 is an integratedcomponent of the present integrated front projection system withdimensions of 36 inches (91 mm) in height, 48 inches (122 mm) in widthand 60 inches (152 mm) diagonal. In this embodiment, when the arm is inits projection position, the projection lens 802 is positioned about 752mm from projection screen 800, about 67.7 mm above the top of projectionscreen 800, and is directed down from horizontal at about 15 degrees.Further, in this embodiment, view region 804 begins about 1000 mm fromprojection screen 800. Projection screen 800 is additionallycharacterized by the parameters set forth in Table B below.

TABLE B Light Spread Horizontal: ≧±60° Vertical: +0°, −52° top ofscreen, to +43°, −20° bottom of screen Peak Gain Between 1.5 and 2.0Surface White, with dry erase capability, or Silver with highest gainAcutance Compatible with projector resolution, e.g., XGA DMD (1024 × 768pixels, 14 μm pitch, 18 mm diagonal) Projected pixel size P = 1.2 mm @85.7X

With regard to pitch of the lenticular grooves 809, a pitch is chosen,p=0.075 mm, to suppress Moiré between the screen structure and theprojected pixels. In this case, the ratio of the projected pixel size,P, and the groove pitch, p, is:

P/p˜n+ ½, where n=16

The structured film 808 has a thickness between 8-10 mils, and isseamless over the screen size of 36 inches (91.4 cm) high by 48 inches(122 cm) wide, with the linear microgroove frequency fixed at 333grooves per inch (13 grooves per mm).

In this exemplary embodiment, with regard to angles, the groove 809 edgeangles and riser angles are referenced to the screen plane. Given thatgroove position is referenced as the vertical distance Y from the top ofthe screen, the lens center (transition) is about Y=168 mm from the topof the screen. In this embodiment, all riser angles are fixed at 82°,and the reflecting groove edge angles F are described by the followingpolynomial equations (all angles are in degrees):

For0>Y<168mm:

F=F ₀ +a(168−Y)+b(168−Y)²

Where:

F₀=+1.143E-2

a=+3.549E-2

b=+6.351E-6

For 168 mm<Y≦921 mm:

F=F₀ +a(Y−168)+b(Y−168)²

Where:

F₀=+4.558E-2

a=+3.46E-2

b=−1.097E-5

Given these equations as describing the angles, Table C below givesangle values for certain selected grooves above and below the lenscenter transition of Y=168 mm.

TABLE C F = 6.134° at Y = 0.5 mm F = 4.158° at Y = 53.5 mm F = 2.073° atY = 110.5 mm F = 0.0292° at Y = 167.5 mm F = 0.0629° at Y = 168.5 mm F =5.347° at Y = 329.5 mm F = 11.649° at Y = 549.5 mm F = 19.87° at Y =920.5 mm

It is further noted that the values and configuration details discussedabove may be modified and changed, as desired, depending upon theparticular projection environment in which the screen is being utilized.

As may be appreciated in FIG. 5, the projection system 100 places theprojection head 106 at an extreme angle and close distance to the screen102, thus minimizing the possibility of the presenter's interference.Placement of the optical head 106 at the end of a radically offsetprojection arm 108 presented unique mechanical and optical challenges.2o Even the lightest and most compact conventional portable projectorsat about 7 lb (3.2 kg), may have leveraged unbalanced strain upon thestructure components. Optically, the throw distance necessary to evenfocus the image would have necessitated a long arm, further creatinglever amplified stresses on the structure. Even if structurally sound,the system would have projected a severely keystone distorted andrelatively small image.

An electronic optical engine includes imaging and electronic components.As better illustrated in FIG. 6, in projection system 100 the arm 108 isa rigid hollow structure. The structure of arm 108 defines an armchamber 122 and allows for the modular and separate placement of a lampcontroller module 118 and an imaging module 120. The lamp controllermodule 118 includes control boards, ballast, and other electroniccomponents. The electronic elements are internally connected through anarray of internal power and data connections. The imaging module 120includes a light source, projection optics, color wheel and imager. Bydistributing components of the projection system along the arm and theframe, a lesser load is placed on the hinge and the arm. Also, a smallerprojector head size becomes possible. Those skilled in the art willrecognize that a variety of different modular arrangements may bepossible within alternative embodiments of the present invention. Forexample, alternatively, components of the electronics module may beplaced inside of frame 104.

A considerable amount EMI/RFI shielding is required in traditionalprojector designs to reduce EM cross talk between the lamp and theelectronic components and to have radio frequency containment. Theseparate placement of electronic components 20 within the arm 108naturally reduces EMI/RFI interference. Furthermore, in the exemplarysystem 100, the power supply and control electronics module 118 isenclosed by a honeycomb structure 124 including a plurality of hexagonalcells 125. The honeycomb structure surrounds imaging module 120 andprovides both EMI/RFI shielding and thermal management characteristics.FIGS. 18 and 19 illustrate details of the honeycomb structure 124. Asdescribed in U.S. Pat. No. 6,109,767, “Honeycomb Light and Heat Trap forProjector”, which is assigned to 3M and hereby incorporated byreference, the shape, orientation, thickness and size of the hexagonalcells may be tuned to attenuate specific electromagnetic frequencies. Inthe present exemplary embodiment, the hexagonal cells 125 are alignedgenerally longitudinally along the arm 108 and are oriented at apredetermined specific angle φ to attenuate high electromagneticfrequencies. The honeycomb structure 124 is an aluminum hexagonal corehaving 0.25-0.0625 inch (0.635-0.159 cm) cell size S, 0.002 inch (about0.005 cm) foil thickness T, and a corrosion resistant coating. Thephysical separation of the electronic components and the honeycombstructure 124 provide sufficient attenuation to reduce the need forother traditional coatings or shields.

The present arrangement also offers an efficient thermal managementsystem. An air intake 126 is located in the housing of the hinge unit110. A fan 130, located in the projection head 106, draws air throughthe air intake 126, through the interior of the hollow projection arm108, cooling the imaging module 120 located therein. The air exits theprojection head 106 through an air outlet 129. Air also may be drawnthrough the projection head 106. The flow of cooling air also may beused to cool other components located in the projector head 106 or aseparate cooling air flow or heat management elements may be employed.

The orientation of the honeycomb structure 124 also is designed to actas a convection heat sink to absorb the thermal energy generated by theelectronic module 118 and transfers the heat by convection into the flowof cooling air drawn by the fan 130. The honeycomb structure is orientedto direct airflow over sensitive components. Different portions of thehoneycomb structure 124 may have different inclination angles to directair flow to different components. The chamber 122 may also includeexterior or interior fins, 127 and 128 respectively, to act as highefficient heat exchangers for both lamp and electronics cooling. Theability to direct the flow of cooling air with the honeycomb structure124 into the interior fins 128 allows for better convection cooling,thus enabling the use of a low CFM fan 130 or even the use of naturallycreated convection. The cooling arrangement offered by the arm and thehoneycomb structure also allows for very low overall power consumptionand low audible noise.

Commercially available electronic front projectors are designed toproject a specified screen diagonal (D) at a specified throw distance(TD). The throw ratio (TR) of i5 a projector is defined as the ratio ofthrow distance to screen diagonal. Magnification is measured as screendiagonal/imager diagonal. Optically, the unobtrusive arrangement of theprojection head 106 of projection system 100 requires that the imagesimultaneously accommodate three very demanding requirements: (1)short-throw distance, (2) high magnification, and (3) large keystonecorrection. To minimize image shadowing, in the present exemplaryembodiment, the projector head 106 is located at a projection angleabout 15° and the arm measures about 30 in (76.2cm). The screen 102 hasa screen diagonal between 42 to 60 inches (about 107-152 cm).Accordingly, the design goals for the exemplary display system 100included (1) a throw distance≦800 mm; (2) a magnification≧60X; and (3)keystone correction for a projection angle˜15°.

Referring to FIG. 6, the projection head 106 includes a lamp unit 132,an imager or light valve 134, condensing optics 136, a color wheel 138,a condensing mirror 139 and a projection lens 140. The projection headmay also include polarization converters (for polarization rotatingimager), infrared and ultraviolet absorption or reflection filters, analternative light source possibly coupled with a lamp changingmechanism, reflector mirrors, and other optical components (not shown).The lamp unit 132 includes a reflector 131 and a lamp 133. The reflector131 focuses the light produced by the lamp 133 through the color wheel138. The beam of light then is condensed by the condensing optics 136and the condensing mirror 139. The now condensed beam of light isreflected off the condensing mirror and is directed towards thereflective imager 134, which in turn reflects the light onto theprojection lenses 140.

The lamp unit 132 includes an elliptic reflector 131 and a highintensity arc 15, discharge lamp 133, such as the Philips UHP type, fromPhilips, Eindhoven, The Netherlands, or the OSRAM VIP-270 from Osram,Berlin, Germany. Other suitable bulbs and lamp arrangements may be used,such as metal halide or tungsten halogen lamps.

In the present exemplary embodiment, the imager 134 comprises a singleXGA digital micromirror device (DMD) having about an 18 mm (0.7 inch)diagonal, such as those manufactured by Texas Instruments, Inc., Dallas,Tex. The color wheel 138 is a spinning red/green/blue (RGB) colorsequential disc producing 16.7 million colors in the projected image. Inalternative embodiments, the color wheel and the imager 134 may bereplaced by different suitable configurations, such as a liquid crystalRGB color sequential shutter and a reflective or transmissive liquidcrystal display (LCD) imager. Those skilled in the art will readilyrecognize that other optical components and arrangements may be possiblein accordance with the spirit of the present invention.

The imager 134 and the lamp 132 may be cooled by the airflow generatedby the fan 130. A further thermal advantage of the arrangement of thepresent embodiment is that the warmer components, such as the lamp, arelocated at an end portion of the cooling air flow path, thus preventingthe intense heat from the lamp from affecting delicate electroniccomponents.

The focus of the lens 140 is preset for optimal resolution on screen102. To provide full keystone correction, the light valve center may beshifted from the projection lens center by an amount equal to theprojection angle. The keystone correction features need not be limitedonly to the optics. Keystone corrected optics, electronic keystonecorrection means, and screen inclination may be combined to achieve asuitable image. In an alternative embodiment, the screen may be motordriven, to reach an inclined projection position at the time that thearm is placed in the open position.

FIG. 7 illustrates a second exemplary embodiment of the presentinvention. The same last two digits in the reference numerals designatesimilar elements in all exemplary embodiments. To decrease the size ofthe light engine even further and to reduce the size and weight ofprojector head 206 and arm 208, lamp 232 and fan 230 are placed withinhinge unit 210 or within frame 204. Power supply and electroniccomponents 218 are located inside frame 204 and behind screen 202. Asequential color wheel 238, a projection lens 240, and condensing optics236, including a condensing mirror 239, remain within the projector head206. A flexible illumination waveguide 242 is channeled through theprojection arm 208 and couples the illumination from the lamp or lightsource 232 to the condensing optics 236. The lamp 232 focuses light intoan entrance aperture 246 of the illumination waveguide 242. The light istransmitted by the illumination waveguide 242 up to an exit aperture245, where the light is then directed through the color wheel 138 to thecondensing optics 236 and 239. In the present embodiment, theillumination waveguide 242 can be a solid large core plastic opticalfiber, such as Spotlight type LF90FB from Sumitomo 3M Company, Ltd.,Japan, or Stay-Flex type SEL 400-from Lumenyte International Corp., ofIrvine, Calif.

Cooling in system 200 is performed in a reverse direction than in system100. The cooling mechanism or fan 230 draws air from the air intake 226located in the projection head 206 and exhausts air through the airexhaust 227 located on the hinge unit 210.

FIG. 8 illustrates a third exemplary embodiment of a projection system300 in accordance with the present invention. The projection system 300includes a projection head 306 mounted along the mid-span of a pivotingarm 308. The projection head 306 is substantially similar to theprojection head 106 in system 100. The image projected by a projectionlens 340 of the projection head 306 is reflected off a mirror orreflective surface 346 onto a screen 302. The arrangement of opticalsystem 300 allows for an increased throw distance and magnificationwhile maintaining the same arm length or for the same throw distance andmagnification with a shorter pivoting arm.

FIG. 9 illustrates a fourth exemplary embodiment of a projection system400 in accordance with the present invention, having a screen 402, aframe 404, a projection head 406, and an arm 408. The projection head406 of the projection system 400 includes a lamp 432 optically alignedwith a transmissive color wheel 438 and condensing optics 436. Afterpassing through the color wheel 438 and the condensing optics 436, alight beam is focused upon a reflective imager 434, which, in turn,directs the light beam towards a retrofocus projection lens 440. Theprojector system 400 includes lamp controller electronics 418 and aseparate modular driver board 448 for the imager 434.

FIG. 10 illustrates a fifth exemplary embodiment of a projection system500 in accordance with the present invention. In the projection system500, the system power supply electronics 519 are positioned inside of aframe 504. A hinge 510 couples an arm 508 holding a projector head 506to the frame 504. Electronic control boards 550 are positioned withinthe arm 508. The projection head 506 includes a lamp unit 532, apolarizer 535, optics 536, a transmissive LCD imager 534, and projectionlens 540, all aligned in a straight optical path. A fan 530 providesventilation. As illustrated in FIG. 11, the arm 508 may be rotated a±90°for storage on the right or the left side.

FIGS. 12 and 13 illustrate the versatility of the projection system ofthe present invention. FIG. 12 illustrates an interactive digitalwhiteboard system 601 including a projection system 600 in accordancewith the present invention and an input device, such as a stylus, 653.The projection system 600 includes integrated electronics for anannotation system 652, as well as LTV, K laser or other type of sensors654. The sensors 654 are calibrated to track the movement of the stylus653 on the surface of the screen. The stylus 653 similarly may includetransmitters and/or sensors to aid in tracking and to coordinate timingor control signals with electronics 652. The screen 602 may be coated toallow for erasable whiteboard use. The integrated electronics 652 mayinclude a CPU.

FIG. 13 illustrates a videoconferencing and/or dataconferencing system701, including a projection system 700 in accordance with the presentinvention. A camera 756, such as a CMOS or CCD camera, is mounted on theprojection head 706 or on the frame 704. The camera 756 may pivot tocapture a presenter or to capture documents placed on the screen 702.Alternatively, additional cameras may be directed to the presenter andto the screen. Again, the screen may be coated to act as an erasablewhiteboard. The camera 756 is directly coupled to a CPU 758 integrallyplaced within the frame 704. A microphone 760 also is placed within theframe 704. Additional electronic modules, such as a tuner, network card,sound card, video card, communication devices, and others may be placedwithin the frame 704.

Those skilled in the art will readily appreciate that elements of thepresent invention may be combined, separately or in one system, toprovide videoconferencing, data-conferencing, and electronic whiteboardfunctions, as well a any other function where a light and compactdisplay system may be useful.

As the system of the present invention is designed to optimize theprojection image at the predetermined projection position, no set-upadjustments are necessary to the optics, mechanics, or electronics andoptimal on-screen performance is consistently offered. The integralstructure of the system 100 allows for easier storage and portabilityand avoids cabling and positioning associated with the use oftraditional projectors.

Those skilled in the art will appreciate that the present invention maybe used with a variety of different optical components. While thepresent invention has been described with a reference to exemplarypreferred embodiments, the invention may be embodied in other specificforms without departing from the spirit of the invention. Accordingly,it should be understood that the embodiments described and illustratedherein are only exemplary and should not be considered as limiting thescope of the present invention. Other variations and modifications maybe made in accordance with the spirit and scope of the presentinvention.

What is claimed is:
 1. A front projection screen, comprising: a backstructured layer formed with a plurality of grooves and operable todirect light into a defined audience view region; and a front diffusinglayer coupled to the structured layer, the diffusing layer formed from amatte polyester film to provide dry erase capability on a front surfaceof the diffusing layer.
 2. The front projection screen of claim 1,wherein the matte polyester film is TEKRA Marnot XL matte Melinexpolyester film.
 3. The front projection screen of claim 1, wherein thestructured layer is formed as an acrylate linear prismatic structurehaving a gloss white coating.
 4. The front projection screen of claim 3,wherein the acrylate linear prismatic structure and the matte polyesterfilm are coupled by lamination.
 5. The front projection screen of claim3, wherein the acrylate linear prismatic structure and the mattepolyester film are coupled by being extruded as a unitary construction.6. An integrated front projection display system, comprising: a frontprojection device; and a front projection screen configured to receivean image from the front projection device, the front projection screencomprising: a back structured layer formed with a plurality of groovesand operable to direct light into a defined audience view region; and afront diffusing layer coupled to the structured layer, the diffusinglayer formed from a matte polyester film to provide dry erase capabilityon a front surface of the diffusing layer.
 7. The integrated frontprojection display system of claim 6, wherein the matte polyester filmis TEKRA Marnot XL matte Melinex polyester film.
 8. The integrated frontprojection display system of claim 6, wherein the structured layer isformed as an acrylate linear prismatic structure having a gloss whitecoating.
 9. The integrated front projection display system of claim 8,wherein the acrylate linear prismatic structure and the matte polyesterfilm are coupled by lamination.
 10. The integrated front projectiondisplay system of claim 9, wherein the acrylate linear prismaticstructure and the matte polyester film are coupled by being extruded asa unitary construction.
 11. The integrated front projection displaysystem of claim 6, wherein the front projection device is coupled to thefront projection screen.
 12. The integrated front projection displaysystem of claim 11, wherein the front projection device is movablycoupled to the front projection screen.
 13. The integrated frontprojection display system of claim 12, wherein the front projectiondevice comprises an arm that is movably coupled to the front projectionscreen, the arm having a non-projection position and a projectionposition.
 14. The integrated front projection display system of claim13, wherein the projection system is an off-axis projection system witha throw ratio of less then about
 1. 15. A method for providing aviewable image from a projection display system, comprising: utilizing astructured layer for a back surface of a projection screen to directlight into a defined audience view region, the structured layer beingformed with a plurality of grooves; and utilizing a front diffusinglayer coupled to the structured layer to provide dry erase capability ona front surface of the diffusing layer, the diffusing layer being formedfrom a matte polyester film.
 16. The method of claim 15, wherein thematte polyester film is TEKRA Marnot XL matte Melinex polyester film.17. The method of claim 16, wherein the structured layer is formed as anacrylate linear prismatic structure having a gloss white coating. 18.The method of claim 17, wherein the acrylate linear prismatic structureand the matte polyester film are coupled by lamination.
 19. The methodof claim 15, further comprising projecting an image to the projectionscreen with a front projection system.
 20. The method of claim 19,wherein the front projection system includes a front projection device,the front projection device including an arm that is movably coupled tothe front projection screen.
 21. The method of claim 20, wherein theprojection system is an off-axis projection system with a throw ratio ofless then about 1.